The invention relates to a pipetting device with at least one attachment for mounting a pipette tip and an ejection device for releasing a pipette tip from the attachment.
Pipetting devices are used in particular in the laboratory for metering liquids. They are drawn into pipette tips through a tip orifice and dispensed. With air cushion pipettes a displacement device for a gas is incorporated in the pipetting device and communicatingly connected to the pipette tip by the attachment. An air cushion is displaced by means of the displacement device, so that liquid is suctioned into the pipette tip and ejected therefrom. The displacement device is generally a cylinder with a piston which can be displaced therein.
The pipette tips are releasably connected to the attachment, so that they can be exchanged after use for a fresh pipette tip. As a result contamination can be avoided during subsequent metering. Single-use pipette tips are available cheaply, made from plastics.
The attachment for fastening pipette tips is frequently a cylindrical or conical projection relative to a base body or a housing, and onto which a pipette tip with a suitable mounting opening or receiver can be clamped. This can take place without grasping the pipette tip by pressing the attachment into the mounting opening of the pipette tip which is ready in a holder.
To avoid contamination of the user, pipette devices comprise an ejection device with a drive device and a throw-off device. By actuating the drive device the throw-off device is displaced, such that it releases the pipette tip from the attachment, without it having to be grasped by the user. Frequently, the drive device has a mechanism which has to be manually actuated by means of an actuation button, in order to release the pipette tip from the attachment. Drive devices are also possible with an electromotive drive. Releasing the pipette tip from the attachment can require increased operating force, in particular with pipette tips which are rigidly clamped onto the attachment. Even with one-channel systems, i.e. pipetting devices which comprise a single attachment for a single pipette tip, this can make ejecting the pipette tip from the attachment difficult or impossible. Particularly high operating force can be required with multi-channel pipette systems which have a plurality of parallel attachments for mounting pipette tips, due to multiple tip ejection forces.
A pipette system with an axially movable throw-off device for releasing a pipette tip from an attachment, a drive device to drive the axial movements of the throw-off device and a pull-means gear, push-means gear or linkage gear transferring an axial drive movement of the drive device into an axial movement of the throw-off device is known from EP 0 992 288 A2. The force exerted by the throw-off device on the pipette tip exceeds the force exerted by the user, whereby the ejection is facilitated.
A pipetting device is known from U.S. Pat. No. 4,187,724 which comprises an attachment for mounting a pipette tip which is a portion of a shaft protruding from a body and which can be rotated in the body. The pipetting device comprises a rotary drive for the shaft. Moreover, the end of the body facing the attachment is constructed as a curved surface. The pipette tip also comprises a curved surface on the mounting end. By actuating a slider the shaft is displaced in a rotational movement, whereby a pipette tip placed on the attachment is rotated with its curved surface against the curved surface of the body, so that on further rotation of the shaft the attachment rotates relative to the pipette tip and the pipette tip is released. In these pipetting devices, the actuation of the ejection device still requires a high operating force. Furthermore, due to the curved surface, the pipette tips are special parts.
Moreover, pipetting devices and accompanying pipette tips are known which comprise an inner shoulder in order to restrict alterations in the mounting force and accordingly the operating force to actuate the ejection device. These pipette systems have the disadvantage that the use of the pipette tips is restricted frequently to the accompanying pipetting devices and vice versa. The user is restricted by this.
Proceeding from this, the object of the invention is to provide a pipetting device which reduces the operating force required to actuate the ejection device. The object is achieved by a pipetting device with the features of claim 1. Advantageous embodiments of the pipetting device are revealed in the sub-claims. The pipetting device according to the invention has a base body; at least one attachment protruding from the base body and axially movably mounted on the base body for mounting a pipette tip, a spring, via which the attachment is supported on the base body, a stop associated with the attachment beyond which the attachment protrudes axially when it is not loaded toward the spring, and an ejection device to release the pipette tip from the attachment which comprises a throw-off device associated with the attachment, the attachment and throw-off device being movable relative to one another, and which comprises a drive device cooperating with the throw-off device and/or the attachment for the relative movement of the throw-off device and the attachment.
In the pipetting device according to the invention, a pipette tip is mounted by axially inserting the attachment into the mounting aperture. The mounting force is then passed into the spring. When the mounting force exceeds a specific amount, the spring is elastically deformed until the pipette tip clamped on the attachment abuts against the stop. As soon as the pipette tip bears against the stop, it can no longer be pushed further onto the attachment. As a result the mounting force of the pipette tip is limited. The mounting force is determined by the spring characteristic of the spring, or a preload of the spring which is possibly present. The spring is designed and optionally biased, such that the pipette tip bears against the stop, precisely when it is positioned with the desired mounting force on the attachment. The mounting force is established, such that the pipette tip is positioned securely on the attachment and provides a seal. As a precisely defined mounting force is reached, it is possible to limit the mounting force to a small amount, where the required certainty of the fit and the seal is precisely given. Thus the mounting force can be markedly reduced relative to conventional pipetting devices, in which an excessive mounting force is regularly used due to unreliability during mounting. Accordingly, in the pipetting device according to the invention, the operating force required to actuate the ejection device is reduced. With manually actuatable ejection devices, stresses on the tendons and muscles of the user are reduced by reducing the operating forces. Ejection devices operated electromotively manage with lower powered motors. According to an embodiment the spring is designed and/or biased such that the attachment can be displaced to such an extent toward the stop by a defined mounting force which can be applied to the attachment by mounting a pipette tip, that the pipette tip bears against the stop.
To release the pipette tip from the attachment, the attachment and throw-off device are axially or rotatably movable relative to one another. The invention includes embodiments in which the throw-off device is arranged fixedly relative to the pipetting device and the drive device exclusively moves the attachment. Moreover, the invention includes embodiments in which the drive devices move the throw-off device and the attachment. In preferred embodiments the attachment is stationary relative to the pipetting device and the drive device only cooperates with the throw-off device, so that solely the throw-off device can be moved by means of the drive device.